Learning SQL will come in handy at any IT job. If you work in data science or data engineering, you will be using SQL daily. Here are some resources to develop your SQL skills.

Interactive websites to learn SQL

SQL Bolt 

SQL Bolt is an interactive website where you can practice writing your SQL code in your browser. You don’t have to install SQL on your local machine.

SQL Zoo

SQL Zoo is another interactive website to learn SQL. Tutorials include SQL Window functions and a section on SQL hacks.

Select Star SQL

Select Star SQL is an interactive book. Each chapter takes about 30 minutes to complete.

StrataScratch

StrataScratch is partially free. It has practice problems and interview questions at top tech companies. In addition to SQL, it’s a great resource for algorithms, system design, statistics, probability, and Python.

BIPP

BIPP is a great resource to learn basic, intermediate, and advanced SQL.

SQL Cheat Sheets

Here are some SQL cheat sheets for quick reference

Basic SQL  Cheat Sheet
Advanced SQL Cheat Sheet

SQL Books

Here are some great books to learn SQL.

SQL: Easy SQL Programming & Database Management For Beginners, Your Step-By-Step Guide To Learning The SQL Database (Felix Alvaro)
SQL Cookbook: Query Solutions and Techniques for All SQL Users (Anthony Molinaro & Robert de Graaf)
SQL in 10 Minutes a Day, Sams Teach Yourself (Ben Forta)